fix: avoid stale serve db connections

[machado144]

Summary

• use a fresh short-lived DB connection for Serve seed and gap-fill jobs
• avoid stale pgx/Cockroach type metadata after schema resets/recreates, which surfaced as cache lookup failed for type ... during enum inserts
• add a regression test that simulates a stale session connection failing while the fresh run connection succeeds

Verification

• manual Serve retest on http://127.0.0.1:8081
• GOCACHE=/tmp/seedstorm-gocache /home/youngestaxe/go/bin/go1.25.10 test ./...
• make test-integration

[github-actions]

StructLint — All checks passed

162 rules validated against .structlint.yaml. No violations found.

_{View full run · Powered by StructLint}